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Supervillains takes note: Even the biggest and the meanest asteroids may not be 100% effective as a doomsday device.
A cosmic impact Powerful enough to eliminate all life on the Earth's surface, large amounts of rock would orbit the sun. Steinn Sigurðsson, a professor in the Department of Astronomy and Astrophysics at Penn State University, said most of these elements would eventually fall back on our damaged and damaged planet.
"This is particularly reassuring," Sigurðsson said last month at the Breakthrough Talk conference at the University of California at Berkeley.
"If you have a sterilizing impact – if you have an afterlife dinosaur killer, something that will fry the whole planet – there is a significant probability that some biota are ejected and return to the planet, gently, quickly enough to reseed the planet, "he added.
Related: Potentially dangerous asteroids (Images)
The existence of such "spatial refuges" is supported by computer simulations recently carried out by Sigurðsson and his colleagues, who followed the trajectories of the rock projected onto the Earth and other rocky planets orbiting the sun.
By the way, this is a relatively small subclass of ejected material; most of the released rock would not reach the exit speed and therefore would come back down quickly. Indeed, scientists believe that the deadliest in the dino-offing impact of 66 million years ago could have been a global fire storm which ignited during the return of the rocks warmed the upper atmosphere of the Earth to about 2,700 degrees Fahrenheit (1,482 degrees Celsius).
Sigurðsson and his team have followed the simulated orbital evolution of the ejecta for 10 million years. They chose this time frame "because there is a meme in the literature that you could keep biota viable [inside a rock in space] Sigurðsson said: "Beyond that, you are trying your luck."
The ejecta begins in a solar orbit similar to that of its original planet and most of the materials eventually resolve. But gravitational tugboats passing planets drive pieces of rocks on different paths.
For example, in the simulations, a few percent of ejecta into orbit went to one of the other rocky planets. We know that happens, of course; scientists have identified more than 100 Meteorites of Mars here on earth. But the scale of the rock exchange in the inner solar system was unexpected, Sigurðsson said.
"It was actually surprisingly high," he said. "There is really a rain of rocks."
Less than 0.1% of the ejecta go to the outer solar system, the kingdom of the potentially habitable planet Jupiter Europa and Saturn satellites Enceladus and Titan, which are also capable of sustaining life.
This may seem like little, but it represents tens of thousands of rocks over the 4.5 billion years of solar system history, according to the team's simulations. And these results represent a conservative estimate, said Sigurðsson.
"The solar system is therefore vulnerable to cross-contamination, and we should be aware of it when we look for life in the external system," he said.
Related: 7 theories about the origin of life
And we will soon look for life, if everything goes as planned. NASA plans to launch a mission to Europe between the early and mid-2020s. Europa Clipper probe will characterize the underground ocean of the moon over dozens of overflights and will also look for places where a lander looking for life can land. (The lander's mission is not yet officially listed in NASA's books, but Congress has asked the space agency to develop it.)
NASA is also planning to develop a Titan drone mission called Dragonflywho would study in detail the atmospheric chemistry of the great moon. The dragonfly could spot any signs of life in the air of Titan, in the form of gas in chemical imbalance. (Dragonfly is one of two finalists, with the CESAR Comet Sampler Recovery Mission, for a middle-class mission launch point in the mid-2020s. The agency is expected to announce its choice by end of the year.)
In addition, a few percent of the ejected rocks are totally outside our solar system, suggesting that life on Earth (or Mars) may have seeded worlds surrounding other stars, said Sigurðsson. Such seeding may have occurred in the other direction as well; some scientists think that life may have arrived on Earth for a long time on board an interstellar object.
These are only speculations, of course; nobody really knows where or how life on Earth startedor where it can be extended. But other research suggests that it is entirely possible for life to make the trip witnessed an impact from one world to the next.
For example, experiments have shown that some bacteria and small animals called tardigrades can survive in the extreme conditions of space. And the powerful impacts that send such beasts on an interplanetary or interstellar trek are not as deadly as you think.
Benjamin Weiss, professor of planetary science at the Massachusetts Institute of Technology, presented research for this purpose at the Breakthrough Talk conference. The work of Weiss and his colleagues suggest that at least some meteorites on the planet Mars have experienced surprisingly low maximum temperatures when they were launched from their planets, which means that they have probably not been sterilized.
And life can probably also survive the journey from space, said Weiss and Sigurðsson.
"I think atmospheric input is basically a non-problem here; it's the easiest part of the problem," Weiss said at a panel discussion at the conference.
So, life can usually go from planet to planet, especially in compact solar systems such as TRAPPIST-1, in which multiple potentially habitable worlds reside end to end.
"You expect that such systems – if they develop life, if life is common – fertilize completely," Sigurðsson said.
Mike Wall's book on the search for extraterrestrial life, "Over there"(Grand Central Publishing, 2018, illustrated by Karl Tate), is out now. Follow him on Twitter @michaeldwall. Follow us on twitter @Spacedotcom or Facebook.
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